Plastic sheet and method of manufacture



June 18, 1946. E. H. LAND PLASTIC SHEET AND METHOD OF MANUFACTURE FiledMay 22, 1942 FIG.

INVENTOR Patented June 18, 1946 PLASTIC SHEET AND METHOD OF MANUFACTUREEdwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation,Cambridge, Mass., a corporation of Delaware Application May 22, 1942,Serial No. 444,143

15 Claims. 1

This invention relates to a composite plastic sheet or film particularlyadapted for use in the production of light-polarizing material andstereoscopic images embodying light-polarizing material, and methods ofmaking said sheet or film. An object of the present invention is toprovide a sheet or film of transparent plastic material whose surfacescomprise molecularly oriented polyvinyl alcohol, the inner portion ofwhich comprises material substantially less hydrophilic than polyvinylalcohol, and particularly such a sheet having the direction of molecularorientation of one surface substantially at right angles to thedirection of molecular orientation of its other surface.

Another object is to provide a transparent sheet or-film comprisingpredominantly a derivative of polyvinyl alcohol, having a layer on 7 onesurface thereof at least partially converted by regeneration topolyvinyl alcohol. and particularly such a sheet which has been treatedto orient the molecules in said polyvinyl alcohol surface layer.

A further object is to provide a composite sheet or film comprising apair of sheets of a transparent polyvinyl alcohol derivative, each ofwhich has an integrally formed surface layer comprising polyvinylalcohol and which are bonded together back to back with said polyvinylalcohol layers outermost and the directions of molecular orientationtherein substantially at right angles t each other.

Further objects are to provide sheets of the above type which have beenstained with a dichroic dye or stain and thereby renderedlightpolarizing. and particularly sheets of the above type which haveright and left eye stereoscopic images reproduced on the oppositesurfaces thereof by means of dichroic dyes or stains.

A still further object is to provide methods for making sheets of theabove type.

Other objects and advantages will in part appear and in part be pointedout in the course of the following detailed description of one of moreembodiments of the invention, which are given as non-limiting examples,in connection with the accompanying drawing, in which:

Figure l is. a diagrammatic view in perspective showing a sheetconstituting an embodiment of the invention;

Fig. 2 is a view similar to Fig. 1 showing a composite sheetconstituting another embodiment of the invention and having dichroicstereoscopic images reproduced thereon;

Fig. 3 is a cross-section showing a composite 2 sheet constituting stillanother embodiment of the invention;

Fig. 4 shows diagrammatically apparatus suitable for use in carrying outsome steps of the process of the invention; and

Fig. 5 shows diagrammatically apparatus suitable for carrying outanother step of the process of the invention.

It has recently been discovered that dichroic light polarizers anddichroic images may be formed by applying a dichroic dye or stain to thesurface of a sheet of suitably molecularly oriented transparent plasticmaterial, such particularly as polyvinyl alcohol. Preferably, in theformation of dichroic stereoscopic images. there may first be provided asheet of plastic material whose outer surfaces comprise polyvinylalcohol molecularly oriented in directions at right angles to eachother, and the images may then be superimposed by printing one on onesurface of the sheet and the other on the other surface with a suitabledichroic dye or stain. The present invention is concerned particularlywith the provision of sheets or films of this type.

In accordance with the present invention, it has been discovered thatimproved sheets of the desired properties may be prepared fromderivatives of polyvinyl alcohol by regenerating or converting a layeron a surface thereof to polyvinyl alcohol, and by suitably stretching orotherwise treating said sheet in appropriate stages of the process toorient the molecules of said layer. Single sheets of this-type may beused advantageously in the production of dichroic light polarizers, andtwo sheets of this type may be bonded together back to back, with thedirections of molecular orientation in their respective layers at rightangles to each other for use in the production of dichroic stereoscopicimages.

The process of the present invention is applicable to substantially alltransparent organic plastics which may be made from polyvinyl alcohol,and hence which may be converted or regenerated to polyvinyl alcoholwhile in sheet form. For the purposes of this description and the claimsherein. the materials falling, within this class will be termedderivatives of polyvinyl alcohol." Preferred materials for the purposeof the invention are from the class consisting of the organic acidesters of polyvinyl alcohol, such for example as polyvinyl acetate. andpolyvinyl formate or the copolymer of p lyvinyl acetate and polyvinylchloride, and the cyclic ethers of polyvinyl alcohol. such particularlyas the acetals and ketals of polyvinyl alcohol. The

term aoetals and ketals of p ly n alcohol"istoheimderstoodasgenerictotheelasofresinsformedirompolyvinylaceiniehythesuccessive orcombinedstepsofhydmlysisandwithaldehydasorketones.

Incanyingoutoneembodimentofthemocessof.theinvenfion.alayerononesm'iaceofasheetofthedesimdbasematerialmayberegm eratedtopolyvinylalcoholbymeansniasuitahlehydrolyzingagent. Inthecaseofpolyvlnyl irydmlymandsimilarmatel'hliasuime ingagentisadilutesoluiionofann'nemlaeidsmhiorexampleassulphuricacidorlnrdrochloricacid.Intheeaseofestersdtherabase oranacidhydmlyzingagentmaybensed. 'Ihesheetisthenpreferablysubjectedtoau'eatment which will orient themolecules in said polyvinyl alcohol layer. For example. the sheet may hestretchedinonedirediiontotwoormore times itsorlginallensmorthepolyvi yalcohollayer may be molecularly oriented by treatment thereofwifliasuitablefl-ietimelement. Inanyevent.thepreferredfonnoftheproductatthlsstlzofthistoftheinveniionmayhedescribed as comprising a sheet Ionnedpredominantlyofatransparent lalcoholderlvative buthavinganintegrallyformed surface layer thereon comprising molecularly orientedpolyvinylalcohol. I

An illustrative example of a product thisiormoftheinveniionisshowncaIIyinHgLwhereinsheetIIasheet or film composed predominantly of aderivative of polyvinyl alcohol. such'for example aspolyvlnylacetalbutonesurfaceoiwhlchhasanimtegrallayerflthereonwhichhasbeenregenerated or converted to polyvinylalcohol. as indicatedbythestippling. Sheet l'isalsorepreseated as havingbeen stretched or otherwise treatedtoorient the moleculesmsuriace l2,asforexampleinthe directionindicatedhyarruw Ii.

Inaccordance with one embodimentoftheinvention, sheet Imaynowbeconvertedto alight polarizer byincorporatingasuitable dichroic yor stain with molecularly oriented polyvinyl 81-- cohol layer It, forexample in the manner set forth inU. S. Patent No. 2,237,567. Such apolariaer will have numerous useful features. Po yvinyl acetal and thesimilar derivatives of polyvinyl alcohol used in the practice of theinvention are in general substantially less hydrophilic than polyvinylalcohol, and since layer It will preferably be relatively thin incomparison with the thickness of sheet II as a whole, the resultingpolarizermadebydyeinglayer I2willbefound less subject to deteriorationby moisture or other forces by which it might otherwise be harmed.Furthermore, such a polarizer will be relatively resistant to curling, adisadvantageous feature of other polarizcrs made from stretched and dyedpolyvinyl alcohol.

Sheet I. may also be used in the production of dichmic light-polarizingimages. referably in the manner indicated in Fig. 2. Sheets 2. and 22represent sheets similar to sheet II in Fig. l, and each having asurface layer thereon converted to polyvinyl alcohol, as indicated bystippling at 24 and 26. The direction of molecular orientation in layer24 is represented by arrow 26 and in layer 25 by arrow 21, and it willbe noted that sheets at and 22 are shown as bonded together back to backwith the directions or molecular orientation in their respective surfacelayers substantially at right angles to each other.

In Fig. 2, layer 24 is represented as havingioxmedthereinanimagellccnsiimtingonehnageiorenmpletheflght-eyeimagaotastereoscopicpair.fimilarlyiayerflhasiormedthemon an image 2! the left-eye imageofastemoseoriepair. Imagesilandflmaybei'orrnedinsaldhyflsbymeansoianysuitahle dichroic dye or stain. sudiforexample as a polydichmicdirectcottonrighteyeofthebhserverwmseeonlyimageflhilayeritandhislefteyewillseeonlyimageHinlayer2lthusproducingathree-dimensional eilect.Itshouldbeunderstnodthatsaidimages maybeformedinlayelsuandliatanydesiredtimeduringasemblyofthedevicethatistosay, the images may be formedseparately before sheets and 22 arebondedtogether. However, according tothe preferred practice, the compositesheetwillfhstbeassembledandtheimagesthen formed thereon. preferablysimultaneously, by applyln toeachsm'iaeethercofa'colloid reliefwhiehhasbcennnhlbedinthedesired dichroicdyeandwhichbelntheremmeoifliedesired images. Itistobehoweventhfltheinventionisnotlimltedtotheuseoftheproducts thereofineonnccfllm withdichroic images, nor toanyparticularwayofformlngsaidimages thereon.

Hg.3showsanotherembodimentoftheinven fionwhiehmaybebymeansoftwosheetsofthetypeshowninl igl. Sheetsiland uml'ig3representtwosheetsofthetypeshown mm. 1. each having a surfacethereof regenerated to p ly l alcohol, ls indicated by thestipplingatuandflmpectlvely. Layerlirepresents an adhesive bondingtogether the convertedsuri'acesotsheetsflandfl,andma.ycom prise, forexample, an additional layer of polyvinylalcoholorothersmhbleadhesivematcrialAcompositesh'eetotthetypeshowninl'ig3 maybeutilisedinavarietyofways.ForexampIeJayusSJand'fl maybeconvertedtolightpolarizersasexplainedaboveinconnectionwith Fig. 1, and the sheets thenlaminated together bymeans-oflayerliinordertoprotectthepolarizingsurfaces. Ifsheets ilandfiaresup rimposed with the directions ofmolecular orienta tion of layers 33 and 31 parallel. the compositesheetwiliserveasallghtpolarizer. Ifonthe other hand the two sheets areput togetherwith -said directions of molecular orientation at rightangles to each other. substantially no visible light will be transmittedby the combination, and it maybeusedasaiilterforusewithinfraredrays. Byvarying the angmar relation between the dimotions of molecularorientation in layers 33 and ll. a filter of any desired density may beobtained. Alternatively. only. one of layers 33 and 34 may be renderedlight polarizing and the other sheet superimposed thereon as aprotection therefor. In still another embodiment. each of layers 33 and34 may have formed thereon one of the images of a stereoscopic pair asexplained above in connection with Fig. 2, and the two sheets may thenbe superimposed and bonded together with the directions of molecularorientation in layers 33 and 34 at right angles. The operation of thisembodiment would be substantially the same as that of the embodimentdescribed in connection with Fig. 2, and'would have the additionaladvantage that layers 30 and 32 would serve to protect the images onlayers 33 and '34. Other modiflcations of this embodiment of theinvention will doubtless be apparent to'those skilled in the art,

affected thereby, and the size and speed of rota-- tion of said drum maybe determined and controlled by the time necessary to regenerate a layerof sufficient thickness upon sheet 40. This time is in turn dependent onthe temperature and concentration of hydrogenions in solution 48.

The extent to which the surface of thesheet is converted will preferablybe controlled rather carefully. It appears also that for preferredresults the surface should be only partially regenerated. that is tosay, some of the surface molecules should be retained in their originalcondi tion, and if this condition is brought about the result will be toinsure a more completely integral structure. In other words, in thepreferred product of this process of the invention. the treated layermay be considered as comprising a mosaic or mixture of polyvinyl alcoholand the original material of the sheet. Ar. an illustrative example forbringing about the preferred results, it may be assumed that sheet 40comprises polyvinyl butyral of the type sold under the trade name"Vinylite X. In this case a suitable hydrolyzing agent is a solution ofequal parts of concentrated sulphuric acid and water, and with such asolu-- tion a suilicient time of treatment is approxi- 6 formed, andthis may be carried out conveniently by stretching the sheet at atemperature sufficient to soften it somewhat, for example 120 C., to

. Fig. 5 shows diagrammatically convenient apparatus for laminating twosheet such as that shown in Fig. 1 to produce composite sheets such asthose shown in Figs. 2 and 3. In Fig. 5, elements I! and I! representrolls of films or a suitable polyvinyl alcohol derivative which has beentreated as for example in the manner described in connection with Fig.4. The sheets from rolls I and 82 may be passed between a pair ofpressure rolls 84 of rubber or other suitable material, and there may beprovided suitable means for app ying a laminating solution to theadjacent surfaces of the two sheets Just before they pass between rolls'4. As shown in Fig. 5, this may comprises trough 85 provided with asuitable aperture 88 along its bottom edge and filled with mately tenminutes at room temperature. It

should be pointed out that in carrying out this embodiment of theprocess of the invention, it is preferred that only one surface of thesheet come in contact with the hydrolyzing solution. and apparatus ofthe type shown in Fig. 2 is accordingly advantageous for the reason thatit permits unilateral regeneration or conversion of the sheet -"withoutfurther precautions. It is tube understood, however, that the inventionis not limited to apparatus of this type nor to this method of treatingonly one surface of the sheet.

When regeneration of a suillcient layer on sheet 40 is completed, thesheet should be washed, and convenient apparatus for this purpose isindicated diagrammatically in Fig. 4 as comprising tanks 50, 52 and 54,throughwhich sheet 40 may be guided as by means of idler rolls 55. Tankrepresents a tank of water. Tank 52 is repre--' sented as containing asolution capable of neutralizing any of the hydrolyzing solutionremaining on the sheet. For example, if solution 48 comprises thesulphuric acid solution mentioned above, tank 52 may contain a 5%solution of sodium bicarbonate. Tank 54 represents a sec- 0nd tank ofwater through which the sheet may be passed before reaching take-up roll58. It will be apparent that if desired there may also I be providedsuitable drying means such as an oven or fan between tank 54 and roll58.

When the foregoing steps are completed, sheet 40 will have approximatelythe characteristics described above in connection with Fig. 1, exceptthat the polyvinyl alcohol layer thereon will not be molecularlyoriented. The next step in this embodiment of the process of theinvention is preferablyto bring about the desired molecular orientationof the polyvinyl alcohol layer lust a suitable laminating solution 88. Aexplained above in connection with Fig. 3, solution 68 may comprise asolution of pblyvinyi alcohol, or in making a composite sheet of thetype shown in Fig. 2 with sheets 10 and 22 of polyvinyl acetal,

solution 48 may comprise acetone or a like solvent. Laminated sheet 10emerging from between rollers 84 maybe considered as corresponding tothe sheets shown and described above in connection with Figs. 2 and 3.

It is to be understood that it is possible to make many othermodifications of the invention besides those above described withoutdeparting from within the scope thereof. It is also to be understoodthat the specific examples are given by way of illustration only, andthat the invention is in no way to be construed as limited thereto. Itshould be particularly noted that any material may be used for thepurposes of the present invention whose characteristics are such thatthe above described process may be carried out thereon to produceproducts having the above described properties, and all such materialsare to be construed as coming within the scope of the invention.

Since certain changes in carrying out the above procesaand certainmodifications in the article which embody the invention may be madewithout departing from its scope, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter or language, might be said to fall therebetween.

What is claimed is:

1. The process comprising treating a surface of a sheet of polyvinylalcohol derivative transformable by hydrolysis to polyvinyl alcohol witha hydrolyzing agentto convert to polyvinyl alcohol a layer on saidsurface without alteration or the central portion of said sheet,predeterminedly orienting the molecules in said layer, andtreatsurfaoeofeachola alcdmlderlvatlve u-ansfonnablebyhydrolysisinpdy ialcohol withmtalteraiionoffliecenlnlporfionof saidsheetsbymflngeachofsaidsm'facs'with.

aagfllhslzetelflngsahlshcetsto orimtflmemsaidlayers,dichroicmaterlalinatleastoneofsaldlayerstorenderitlight-polarlzingandbonding said sheetstoetherwifllthedlredimsofmoleculsr orlentatlm in said layers suhstaniialbat right anglestoeachotherandwlthslldm'lentedlay in inxtaposed'relatlon.

3. Anariicleofmanufamn'eaunitaryplasiiesheaasrrface ofsaldsheetccmprisingmoleculariyodmtedpolyvmlalcdnl and a body portio of said sheetthe surfaces thereof mnsparmtolyvinylalcoholderlvaiivechunmllymmformabletopobvinyalcolflslidpmtlonshehig byaportlmcopolymer molecules of said derivativevinyl alcohol, said molecules invinylalcohol'contentinthedirecilmiofsald 5.Acomposlte plasticof-unitaryplastic sheets. asurface portion of each of said unitarysheets comprising molecutions of molecular orientation-of said surfaceportions being substantially at right angles to each other.predetermined areas of each of said oriented polyvinyl alcohol surfaceshaving dichroic material incorporated therein, the dichroic areas ineach of said sheets forming, in combination. a predetermined image, saidimages being respectively left-eye and right-eye images of apredetermined stereoscopic pair.

6'. A composite plastic sheet comprising a pair of unitary plasticsheets. a surface portion of each of said unitary sheets comprising Plyvinyl alcohol and a body portion of each of said unitary sheetsintermediate'the surfaces thereof comprising a transparent polyvinylalcohol derivative chemically transformable to polyvinyl alcohol, saidportions of each said unitary sheet being interconnected by a portioncomprising coorlentedsurfacesald 8 polymermoleeulesoisaldderivailvemolecules and vinyl invlnylalilcnofeachofsaldunitary sheets intermediatethe surfaces thereof comprising a transparent polyvinyl alcoholderivative chemically transformabletopolyvhiylalcohoLsaldporilonsofeaehsaidnnltarysheetbeingmterconnectedby copolymermoleculesof fldderivaflvaandvinylalcdiol. said molecules increasinginvlnylalcoholcontentinthedirccflonofthemnleailadyorientedsufiacethemodiatethesnrfacesthereofcomprisingatnnsthe.direction of moleculesofsaidacet&l

vinylslcohoLsaldmolecllles alcohol contmtmfliedlrectionofsaid orientedsm-taoesaioorientedpolyv n l alcohol surface alcohol and a body portionmediate the surfaces thereof comprising a transparent polyvinyl acetal.said portiom being interconnected by a portion comprising copolymer andvinyl alcohol. aid molecules in vinyl alcohol content infliedirectionofsaidorientedsurface,saidoricnted polyvinyl alcoholsurface having dichrolc material inthereln. 10. An article ofmanufacture comprising a unitary plastic sheet. a surface portion ofsaid sheet comprising molecularly oriented polyvinyl alcohol and a bodyportion of said sheet intermediate the surfaces thereof comprising atransparent plastic material formed of an organic acid ester ofpolyvinyl alcohol, said portions being interconnected by a portioncomprising co olymer molecules of said ester and vi yl alcohohsaidmolecule increasing in vinyl alcohol content in said orientedsurface,,said oriented polyvinyl alcohol surface having dichroicmaterial incorporated therein.

11. An article of manufacture comprising a unitary plastic sheet, asurface portion of said sheet comprising molecularly oriented polyvinylalcohol and a body portion of said sheet intermediate the surfacesthereof comprising polyvinyl acetate, said portions being interconnectedby a portion comprising copolymer molecules of said polyvinyl acetateand vinyl alcohol, said molecules increasing in vinyl alcohol content inthe direction of said oriented surface, said oriented polyvinyl al- Ihol and a body portion of said sheet intermediate the surfaces thereofcomprising a transparent cyclic ether of polyvinyl alcohol, saidportions being interconnected by a portion comprisin copolymer moleculesof said ether and vinyl alcohol. said molecules increasing in vinylalcohol content in the direction of said oriented surface. predeterminedareas of said oriented polyvinyl alcohol surface having dichroicmaterial incorporated therein, said areas forming, in combination, a

" predetermined design.

13. An article of manufacture comprising a unitary plastic sheet, asurface portion of said sheet comprising molecularly oriented polyvinylalcohol and a body portion -of said sheet intermediate the surfacesthereof comprising a transparent polyvinyl acetal, said portions beinginterconnected by a portion comprising copolymer moleculesof said acetaland vinyl alcohol, said molecules increasing in vinyl alcohol content inthe direction of said oriented surface, predetermined areas of saidoriented polyvinyl alcohol surface having dichroic material incorporatedtherein. said areas forming, in combination, a predetermined design.

14. An article of manufacture comprising a unitary plastic sheet, asurface portion of said sheet comprising molecularly oriented polyvinylalcohol and a body portion of said sheet intermediate the surfacesthereof comprising a transparent plastic material formed of an organicacid ester of polyvinyl alcohol, said portions being interconnected by aportion comprising copolymer molecules of said ester and vinyl alcohol,said molecules increasing in vinyl alcohol content in the direction ofsaid oriented surface, predetermined areas of said oriented polyvinylalcohol surface having dichroic material incorporated therein, saidareas forming, in combination, a predetermined design.

15. An article of manufacture comprising a unitary plastic sheet, asurface portion of aid sheet comprising-molecularly oriented polyvinylalcohol and a body portion of said sheet intermediate the surfacesthereof comprising polyvinyl acetate. said portions being interconnectedby a portion comprising copolymer molecules of said polyvinyl acetateand vinyl alcohol, said molecules increasing in vinyl alcohol content inthe direction of said oriented surface, predetermined area of saidoriented polyvinyl alcohol surface having dichroic material incorporatedtherein, said areas forming. in combination, a predetermined design.

EDWIN H. LAND.

